The present invention relates to the liquefaction of carbonaceous materials, and more particularly to a method for the structural degradation and/or hydrogenation of carbonaceous material with a metal carbonyl or a low valent complex of the transition metals under alkaline conditions in the presence of water gas to form liquid products.
With the present world wide emphasis on the energy crisis and increasingly diminishing supplies of readily produceable, naturally occuring petroleum oil and gas reserves, increased attention by both governmental and private organizations is being given alternate energy sources.
Due to the vast resources of coal and other carbonaceous materials available for development in the United States and other countries, it appears that these resources will play an important role in energy supply for the future. However, a significant proportion of the world's coal supply contains a relatively large amount of heteroatoms, such as sulfur and nitrogen, which lead to air pollution and handling problems upon utilization of the raw coal as an energy source. For this reason, processes for obtaining a clean fuel from raw coal are becoming increasingly attractive.
Several processes are known in the art for beneficiating solid carbonaceous materials, such as coal, to reduce impurities. For example, U.S. Pat. Nos. 3,938,966; 4,098,584; 4,119,410; 4,120,665; 4,146,367; and 4,175,924 relate to such processes.
In addition to the use of beneficiated coal, considerable attention has been given to processes for the gasification of liquefaction of coal to produce petroleum-like oils and gaseous products. Coal liquefaction processes exhibit an advantage over coal gasification processes in that the liquid products of a coal liquefaction process generally have higher energy densities, resulting in mining transportation, storage and utilization savings. Thus, there exits an urgente need for the development of liquefaction processes which are capable of providing liquid fuel products in an economical manner.
The essence of a coal liquefaction process is the structural degradation of, and/or the addition of hydrogen to, a carbonaceous material, with heteroatom removal being an important consideration. In theory, for example, an increase in the hydrogen content of coal of about 2 to 3 percent may result in the production of heavy oils, while an increase in the hydrogen content of coal of about 6 percent or more may result in the production of light oils and gasoline. Present methods for the liquefaction of coal generally include pyrolysis, solvent extraction, direct hydrogenation and indirect hydrogenation. Pyrolysis processes are frequently unattractive due to the high energy inputs required to thermally break down the coal molecule. Solvent extraction utilizes a hydrogen donor solvent system which generally requires a separate step and facilities for catalytic hydrogenation of the solvent system. Indirect liquefaction generally involved reacting coal with steam and oxygen at high temperature to produce gas consisting primarily of hydrogen, carbon monoxide and methane, and then catalytically reacting the hydrogen and carbon monoxide to synthesize hydrocarbon liquids by the Fischer-Tropsch process. Indirect liquefaction processes therefore involve multiple process steps requiring relatively large energy inputs and expensive process facilities. Direct liquefaction processes typically involve the hydrogenation of coal particles with a solid catalyst, such as on a fixed bed catalyst or an ebullated bed catalyst. The use of solid catalyst systems has resulted in additional problems, since it is difficult to obtain contact between the solid phases of the coal and catalyst, and solid catalytic processes frequently suffer from catalyst poisoning.
As can be seen from the foregoing, there are many problems associated with the production of hydrocarbon liquids from solid carbonaceous materials, including the need for expensive high pressure and temperature equipment, relatively low yields which are obtained under economically feasible temperature and pressure conditions, catalyst losses, and the like. However, one of the largest problems hindering commercial development of coal liquefaction processes is economic, due principally to the high cost of hydrogen and capital costs associated with high pressure and temperature equipment. In current practices, the main source of hydrogen is from hydrocarbons, including natural gas, LPG, naptha, etc. Regardless of the source, the high cost of hydrogen presently makes coal liquefaction economically prohibitive, even in relationship to the high cost of natural crude oil.
In order to overcome the foregoing problem, it has been suggested that the hydrogen requirements for a coal liquefaction process could be obtained from the water gas shift reaction by reacting carbon monoxide and water (i.e., water gas) to form hydrogen and carbon dioxide. Previously suggested catalysts for this reaction in connection with coal liquefaction processes have been primarily solid catalysts such as metal oxides, metal chlorides, metal sulfides and the like, and various combinations of these catalysts. However, these processes have been found to require relatively high temperature and pressures, and to suffer from catalyst poisoning and relatively low yields.
It has now been found that hydrocarbon liquids can be obtained in relatively high yields from carbonaceous materials by contacting the carbonaceous materials with a liquefaction facilitating agent, such as a metal carbonyl or a low valent complex of the transition metals, and water gas under alkaline conditions to form a reaction mixture, and then heating the reaction mixture to a sufficient temperature and pressure to obtain the hydrocarbon liquids. Treatment according to the present invention can additionally result in the reduction or removal of sulfur, nitrogen and similar heteroatoms, thereby providing a clean burning liquid fuel energy source.